1. Field of the Invention
The present invention relates to a laser package for high frequency applications and, more particularly, to a multilayer ceramic laser package which includes a multilayer microwave input connection capable of providing laser operation in the gigabit per second range.
2. Description of the Prior Art
Associated with the continuing developments in the field of optical communication systems is a need for improved packages to house the various optical devices. For example, optical systems as presently contemplated will contain active optical sources and detectors, both of which are expected to require a hermetic housing to protect the optical devices from attack by deleterious contaminants in the ambient, such as moisture in the atmosphere. Inasmuch as optical signals exit or enter the hermetic housing via optical fibers, some means to hermetically seal the fiber to the housing will be required. There exist many arrangements in the prior art which have been developed to provide these required hermetic packages. One exemplary arrangement is disclosed in Camlibel et al U.S. Pat. No. 4,119,363 issued on October 10, 1978. In the Camlibel et al arrangement, an optical fiber is hermetically sealed to a metal housing containing an optical device by threading and centering the fiber through a thin walled metal tube, filling the tube with solder and allowing it to cool. The solder, upon solidifying and cooling, squeezes against the fiber and forms a thermetic seal. The tube-fiber assembly is inserted through an aperture in the housing wall, the fiber is aligned with the optical device and then the tube is soldered to the wall. An alternative hermetic package for optical devices is disclosed in W. H. Dufft U.S. Pat. No. 4,296,998 issued on October 27, 1981. A metallic sealing cap is affixed to the body for hermetic sealing. The encapsulation is completed by evacuating the inner chamber and back-filling with nitrogen.
One factor used to measure advancement in the field of optical communication systems is the bit rate capability of the system. Continual increases in bit rate is an ever-present goal to optical system designers. As the bit rates exceed 500 Mb/s and approach the gigabit range, problems in providing the input signal to the laser with conventional electrical contacts develop. These conventional contacts begin to exhibit such a large parasitic inductance that it is not possible simply to connect a high bit rate signal source directly to the laser. Borrowing from microwave technology, a coaxial connection may be utilized in place of the electrical connection between the input source and the laser. R. E. Cardianl U.S. Pat. No. 4,309,717 issued on January 5, 1982 discloses such a coaxial input arrangement. As disclosed, a conventional coaxial line is inserted through a standard metal laser package, hermetically sealed in place, and connected to the laser. Although this arrangement solves the problem associated with standard electrical connections at high bit rates, the package itself is bulky, expensive and relatively difficult to manufacture.
An article entitled "Design of a Solid State Laser Hybrid Package" by M. Spector appearing in the International Journal for Hybrid Microelectronics, Vol. 5, No. 2, November 1982 at pp. 172-174 discusses in detail the technological challenges associated with package laser devices for high frequency applications. Dr. Spector describes in particular a new hybrid structure (the GTE TEC-PAC), which is a hermetic laser package of narrow design to keep the input electrical leads as short as possible, and thus reduce their associated parasitics. As discussed in the article, the limiting factor for the design is the overall width of the thermo-electric cooler mount of the laser device. Therefore, the lead lengths for this arrangement will eventually dictate a maximum input signal frequency. Futher, the continual re-design of this standard package to fit high frequency applications results in increasingly expensive packages. Thus, a need remains in the prior art for a laser package capable of accommodating optical transmission at high bit rates (on the order of 500 Mb/s to at least 5 Gb/s) which is rugged, inexpensive, versatile, and relatively simple to manufacture.